Frontier rear suspension mod needed?

For now I need to make my '00 Nissan Frontier (2.4 4cyl, 5 speed, 85k) work best for my business. Between a topper/bedshell and all my LCO equipment I'll have around 500-600lbs loaded back there. Should I make any modifications for this much weight? I will be upgrading my shocks...

Thank you.

---------------------------------------------------~ cut it high ~ let it fly ~
---------------------------------------------------Some folks are so contrary that if they fell into a river,
they'd insist on floating upstream.
~ Josh Billings

---------------------------------------------------~ cut it high ~ let it fly ~
---------------------------------------------------Some folks are so contrary that if they fell into a river,
they'd insist on floating upstream.
~ Josh Billings